The present invention relates to a clamping device for grasping a workpiece to secure the workpiece during subsequent steps of manufacture. The invention is particularly useful for grasping and hanging metal sheet of various thicknesses during thermal heat treatment processing steps.
During the process of heat-treating metal sheet in a furnace, in order to ensure that the metal sheet is evenly heated and uniformly reaches the desired heat treatment temperature, it is advantageous to hang the metal sheet vertically from a rack. As many metal sheets as can fit into a furnace are fitted with one or more clamping devices, and suspended vertically from a rack. The rack, with the clamped metal sheets, is placed into a furnace for heating. Such heating is termed in the art as a vertical heat treat process.
Various clamping devices are known in the art. An apparatus for transporting sheets of glass in a vertical position is described in U.S. Pat. No. 4,240,660. The apparatus has suspension tongs, a carrying strap from which the tongs are suspended and a supporting beam mounted to a trolley.
A clamp device and a clamping system for welding sheet metal are taught in U.S. Pat. No. 6,129,345 and U.S. Pat. No. 5,932,117, respectively.
A latch fastener mechanism for thin sheet materials is described in U.S. Pat. No. 6,237,970 B1. More particularly, the invention relates to a simplified form of connector for ready installation that provides a disengageable clamping action between the parts being held together.
A clamp consisting of a clip and an actuating member is described in U.S. Pat. No. 5,052,644. The clamp of this invention is used for holding flat thin objects together.
U.S. Pat. No. 5,897,087 relates to a surgical apparatus for retracting anatomy to provide exposure of a surgical site. A cam tightened universal joint clamp is described.
A clamping and holding device, which is particularly useful for mounting umbrellas and the like to patio chairs, is taught in U.S. Pat. No. 5,478,041. A first and a second clamping arm are pivotally connected to one another to engage an article. A cam, cam follower and locking member or nut and bolt system prevents the inadvertent opening of the clamping arms.
The clamping device of the current invention finds particular utility in the field of metal or metal alloy heat treating. Metal heat treating typically involves the steps of heating the metal or metal alloy to a predetermined metal heat treatment temperature, holding or xe2x80x9csoakingxe2x80x9d the metal or metal alloy at a predetermined metal heat treatment temperature for a predetermined metal heat treatment length of time, and cooling the metal alloy. It is recognized by practitioners of the art that these steps can be repeated in various combinations which may include several predetermined metal heat treatment temperatures and several predetermined metal heat treatment lengths of time in order to obtain various desired properties, such as but not limited to, strength and corrosion resistance. It is further known in the prior art that metal heating and cooling rates can be varied to alter properties of the metal or metal alloy. It may be particularly useful to rapidly cool the metal or metal alloy after it has been exposed to a predetermined metal heat treatment temperature. A known method for rapid cooling the metal or metal alloy is to remove the metal or metal alloy workpiece from a metal heat treatment furnace, followed by immersing the workpiece in a water bath. This process is referred to by practitioners of the art as xe2x80x9cwater quenching.xe2x80x9d
Referring now to drawings in FIGS. 1-3, a known clamping device 10 used in the field of metal heat treating is presented. FIG. 1 is a front view drawing of the known clamping device 10, FIG. 2 is a side view of the same known clamping device 10 and FIG. 3 is a top view of the known clamping device 10. The known clamping device 10 is comprised of: (a) a hanging portion 11; (b) a clamp portion 12 extending from the hanging portion 11, with the clamp portion having a bracket 13 and a first clamping surface 14; and (c) a wedge 15 having a second clamping surface 16 that is parallel with respect to the first clamping surface 14, and is slideably mounted in the bracket 13 of the clamp portion 12. The hanging portion 11 allows for hanging the clamping device 10 vertically on a rack (not shown). The metal sheet 20 for heat treatment is positioned in the known clamping device 10 so that the upper edge 21 of the metal sheet 20 is between the first clamping surface 14 and the second clamping surface 16. The wedge 15 is then hammered or driven into the clamp portion 12 so that the metal sheet 20 for heat treatment is held in the clamping device 10 by compressive and frictional forces between the first clamping surface 14 on the clamp portion 12, and the second clamping surface 16 on the wedge 15.
A sufficient number of clamping devices 10 are used to secure the metal sheet 20 to the rack. For example, a xc2xc inch thick by 80 inches wide by 250 inches long metal sheet 20 would be oriented in the vertical direction by securing clamping devices 10 on the 250-inch dimension on the xc2xc inch thick upper edge 21 of the metal sheet 20. A typical sheet is hung with about 15 clamping devices mounted along the 250-inch edge. More or fewer clamps may be used depending on the weight of the sheet.
The known clamping device 10 for heat treating metal sheets 20, and the method of using the known clamping device 10, have several drawbacks. The process of driving or hammering the wedge 15 to clamp a large metal sheet 20 produces high noise levels. The metal sheet 20 resonates like a drumhead, and can potentially cause hearing loss to individuals in the vicinity, unless the individuals are wearing adequate hearing protection. The use of a hammer in a repetitive manner in an uncomfortable position over time can result in cumulative motion injury to the worker.
In addition to operator safety concerns associated with the known clamping device 10, the known clamping device 10 does not hold the metal sheet 20 well in all cases, and can cause damage to the metal sheet 20. The known clamping device 10 relies on compressive and frictional forces that are established between the first clamping surface 14, the metal sheet 20 and the second clamping surface 16, as the wedge 15 is hammered into the clamp portion 12. The compressive forces from the driven wedge 15 can cause the first 14 and second 16 clamping surfaces to embed in the metal sheet 20 during the heat treatment process.
When the clamped metal sheet 20 is removed from the furnace, it may be immersed in a water bath, which can have a temperature anywhere between near the ambient temperature or the boiling temperature. This process is called xe2x80x9cwater quenching.xe2x80x9d After the metal sheet 20 is water quenched, because of thermal contraction, it shrinks from the known clamping device 10 and some of the compressive force from the driven wedge 15 is lost. As a result, the prior art known clamping device 10 can slip off the metal sheet 20.
Thus, a need exists for a clamping device for vertically suspending metal sheet during heat treatment that does not present potential occupational safety hazards to worker, that does not damage the metal sheet, and is reliable in holding the metal sheet through all required operations of the manufacturing process.
Accordingly, it is an object of this invention to provide a clamping device to grasp and vertically suspend metal or metal alloy sheet of various thicknesses during a thermal processing step, or any processing step that is benefited by suspending the metal sheet in a vertical orientation.
Another object of this invention is to provide a method for grasping and vertically suspending metal or metal alloy sheet of various thicknesses during a thermal processing step, or any processing step that is benefited by suspending the metal sheet in a vertical orientation.
A further object of this invention is to provide a clamping device for vertically suspending metal or metal alloy sheet that remains clamped during rapid thermal changes that occur, for example, when hot metal or metal alloy sheets are quenched by immersion in a water bath.
Yet another object of this invention is to provide a method for clamping metal or metal alloy sheet that does not result in high noise levels and/or poor ergonomics that could cause physiological injury to operators and others near the clamping operation.
While a principal object of this invention is to provide a clamping device for use with metal or metal alloy sheet, it is recognized that the clamping device of this invention could be made to a size that could accommodate other forms of wrought or cast metal, such as but not limited to castings, forgings, plate, sheet, rod, bar, tube, wire, and structural shapes, such as but not limited to, I-beams, H-beams, channels, angles tees, and zees. Further, the clamping device could be used for grasping and suspending product forms such as for example wheels, bumpers, vehicular frame rails, boat hulls and aerospace wing struts, while these undergo various processing or finishing steps. These forms and other forms of metal are known to those skilled in the art. Therefore, the phrase metal or metal alloy sheet, as used herein, should be interpreted to include any metal or metal alloy workpiece that could be suspended by the clamp of this invention.
Furthermore, it should not be inferred that the clamping device of the current invention should be limited to clamping forms of metals and metal alloys, but it should be recognized that the clamp of this invention could be used for suspending a workpiece made of other materials, such as but not limited to plastics, composites, and laminates.
The objects of this invention are achieved by providing a clamping device for grasping and suspending a workpiece. A preferred embodiment of the clamping device includes: a clamp body, an eccentric wedge, and an eccentric cam. The clamp body further includes: at least one slotted arcuate spring end portion; an intermediate spring spreading portion contiguous with and extending from the slotted arcuate spring end portion, with the intermediate spring spreading portion having an eccentric bore; a jaw end portion contiguous with and extending from the intermediate spring spreading portion, with the jaw end portion comprising a jaw clamping surface and a bracket, with the bracket having a beveled sidewall wherein the jaw clamping surface and the bracket define a jaw opening; and a suspending means attached to the intermediate spring spreading portion. The eccentric wedge is slideably mounted in the bracket. The eccentric cam is rotatably disposed within the eccentric bore.